Technical Field
The invention relates to an air spring. In particular, the invention relates to an air spring for use in vehicular or industrial applications to support a load, and includes gas struts and wheels.
Description of Related Art
Air springs were developed by Firestone® in the late 1930s as a more efficient spring, or vibration isolator, for use in vehicle suspension systems. See for example U.S. Pat. No. 2,208,537 which is incorporated herein by reference. Airide® springs, as the Firestone® air springs were named, provided the means for a suspension to reduce the amount of road shock and vibration transmitted into a vehicle.
In the early 1950s, after many years of experimentation and product development, air sprung buses went into production. The success of air springs in bus applications spurred new interest in truck and trailer applications, as well as industrial shock and vibration isolation uses, and actuator uses.
Consequently almost all buses and many trucks and trailers on the road today now ride on air springs. Air springs are becoming more common in automotive applications and in industrial applications too.
It is known that a direct relationship exists between the spring rate and natural frequency of an air spring and isolation effectiveness.
Generally, the lower the spring rate or natural frequency, the better the isolator.
For example, a double convoluted type air spring usually has a lower spring rate and natural frequency than a single convoluted type at a given pressure. It is known to lower the spring rate and natural frequency, and hence increase the isolation effectiveness, of an air spring by adding an auxiliary reservoir. Of course, there must be free flow of air between the air spring and the reservoir and the reservoir should be mounted as close as possible to the air spring.
Using reservoirs is expensive, bulky and heavy and increases maintenance costs of a load-bearing system.
The invention aims to lower the spring rate of an air spring while mitigating or eliminating one or more of the aforesaid disadvantages of the known art.